If you're like me living in Bengaluru and getting to airport in either extreme - late (more often) Or too early (today's topic)... Your wasted time of life have my condolences!
After travelling so many times (to airport rather than taking off in flights), I found some interesting time consuming way to not get bored (apart from spending time watching people in lounge)
1. Explore foreign/antique shops - They have always surprised me with some of the items which I have never seen in life. But make sure you don't visit it too often to have your face recognised by the shopkeeper (unless you buy things, unlike me).
2. Tracking ground team movement - This might sound boring at first but, have you ever wondered about those colorful criss cross lines on roads? Maybe next time when you reach early enough, try decoding it!
3. Art display - Almost every major airport (at least in India) has a display of vivid art and culture of the place and people. It's worth multiple visit as it just gets better as you understand more and more about the motivation about the art.
4. Find all the boarding gates - It might sound stupid and tiring (specially if you're in New Delhi airport), but has saved me from missing flights when I am just on time (or a little late). Apart from route knowledge, you might find some interesting food joint.
5. Finding pseudo hidden places - Be like a Galileo and set sail to know about the airport. For e.g. try to find the place where you should complain, in case your luggage was broken in transit, free try-out food joints, comfy couch, body massager pit stops, etc. The list goes endless and I can assure you to find something new everytime you visit any airport (unless you're flying everyday)